The aim of the study was the characterization of extended spectrum beta-lactamases (ESBLs) and quinolone resistance in cefotaxime-resistant coliform isolates from a wastewater treatment plant (WWTP). ESBLs were detected in 19 out of 24 isolates (79%) from raw water and in 21 out of 24 isolates (87.5%) from treated water, identified as Klebsiella pneumoniae and Escherichia coli. Molecular characterization of ESBLs and quinolone resistance showed allele profiles CTX-M-15 (3), CTX-M-3 (5), CTX-M-15+qnrB1 (1), CTX-M-3+qnrB1 (1), CTX-M-15+aac-(6')-Ib-cr (4), and CTX-M-15+qnrB1+aac-(6')-Ib-cr (7). A double mutation S83L and D87N (GyrA) and a single mutation S80I (ParC) were detected in ciprofloxacin-resistant E. coli isolates. In K. pneumoniae, mutations S83I (GyrA)+S80I (ParC) or single S80I mutation were detected in ciprofloxacin-resistant isolates, and no mutation was observed in ciprofloxacin-susceptible isolates. bla(CTX-M), qnrB1, and aac-(6')-Ib-cr were found, respectively, in these genetic environments: ISEcp1-bla(CTX-M)-orf477, orf1005-orf1-qnrB1, and Tn1721-IS26-aac-(6')-Ib-cr-bla(OXA-1)-catB4. bla(CTX-M-15) was located on IncF plasmid in E. coli and bla(CTX-M-3) on IncL/M plasmid in both species (E. coli and K. pneumoniae). E. coli isolates were affiliated to the phylogroups/MLST: D/ST405 (CC405), A/ST10 (CC10), A/ST617 (CC10), and B1/ST1431. K. pneumoniae isolates belonged to phylogroup KpI and to sequence types ST15, ST17, ST36, ST48, ST54, and ST147. The study showed a multi-drug resistance at the inflow and outflow of the WWTP, with ESBL production, plasmid-mediated quinolones resistance, and mutations in topoisomerases. The findings highlight the similarity of antibiotic resistance mechanisms in the clinical setting and the environment, and the role of the latter as a source of dissemination of resistance genes.
